4FNF DOUBLY EXCITED AUTOIONIZING SERIES IN BARIUM
Graaff, R.J. de
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In a two-step pulsed-laser atomic-beam experiment we have studied doubly excited 4fnf series of barium with energy of approximately 11 eV above the atomic ground state (6s2) and 6 eV above the first ionization limit (6s). Starting from 5d2(3)F3, 1G4 metastable states, 4f5/2n'f J = 2-6 (9 less-than-or-equal-to n' less-than-or-equal-to 46) states and 4f7/2n''f J = 3-6 (n'' = 19, 20, 21, 25, and 40) states were excited using intermediate 5dnf autoionizing Rydberg states. The 4f5/2n'f J = 2-6 states strongly interact with 4f7/2n''f J = 2-6 (8 less-than-or-equal-to n'' less-than-or-equal-to 20) and 7pn'''f J = 2-5 (6 less-than-or-equal-to n''' less-than-or-equal-to 10) states. The excitation spectra were analyzed and interpreted using multichannel quantum-defect theory as well as a limited Slater-Condon analysis. The quantum defects of the 4fnf series are large (0.5-1.4), which is an indication for considerable two-electron correlation effects.